[clang-tools-extra] [clang-tidy] In C++17, callee is guaranteed to be sequenced before arguments. (PR #93623)

[Kefu Chai via cfe-commits]

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@@ -110,15 +117,32 @@ bool UseAfterMoveFinder::find(Stmt *CodeBlock, const Expr *MovingCall,
   BlockMap = std::make_unique<StmtToBlockMap>(TheCFG.get(), Context);
   Visited.clear();
 
-  const CFGBlock *Block = BlockMap->blockContainingStmt(MovingCall);
-  if (!Block) {
+  const CFGBlock *MoveBlock = BlockMap->blockContainingStmt(MovingCall);
+  if (!MoveBlock) {
     // This can happen if MovingCall is in a constructor initializer, which is
     // not included in the CFG because the CFG is built only from the function
     // body.
-    Block = &TheCFG->getEntry();
+    MoveBlock = &TheCFG->getEntry();
   }
 
-  return findInternal(Block, MovingCall, MovedVariable, TheUseAfterMove);
+  bool Found = findInternal(MoveBlock, MovingCall, MovedVariable->getDecl(),
+                            TheUseAfterMove);
+
+  if (Found) {
+    if (const CFGBlock *UseBlock =
+            BlockMap->blockContainingStmt(TheUseAfterMove->DeclRef)) {
+      // Does the use happen in a later loop iteration than the move?
+      // - If they are in the same CFG block, we know the use happened in a
+      //   later iteration if we visited that block a second time.
+      // - Otherwise, we know the use happened in a later iteration if the
+      //   move is reachable from the use.
+      auto CFA = std::make_unique<CFGReverseBlockReachabilityAnalysis>(*TheCFG);
+      TheUseAfterMove->UseHappensInLaterLoopIteration =
+          UseBlock == MoveBlock ? Visited.contains(UseBlock)
+                                : CFA->isReachable(UseBlock, MoveBlock);
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tchaikov wrote:

`CFGReverseBlockReachabilityAnalysis` comes with two member variables of `llvm::BitVector` and `llvm::DenseMap<>`, which could be potentially too large to put on the stack, i thought. that's why i allocated it on heap. but if you believe it's safe to do so. will allocate it on stack.

https://github.com/llvm/llvm-project/pull/93623